1. Field of the Invention
The present invention relates to a magnetoresistive element, magnetoresistive head and magnetic recording/reproducing apparatus and, in particular, a magnetoresistive element for reading an information signal recorded on a magnetic recording medium, a magnetoresistive head, and a magnetic recording/reproducing apparatus.
2. Description of the Related Art
Conventionally, there has been disclosed a magnetic reading converter called an magnetoresistive sensor or magnetoresistive head as a component of a hard disk drive. These can read data from a magnetic surface with a large linear density.
The magnetoresistive sensor detects a magnetic field signal according to a resistance change as a function of intensity and direction of a magnetic flux detected by a read element. Such a conventional magnetoresistive sensor operates according to the effect of anisotropic magneto resistance (AMR) in such a way that a component of resistance of the read element changes in proportion to the square of the cosine of the angle between the magnetization direction and the sense current direction flowing in the element. The AMR effect is detailed in D. A. Thompson, xe2x80x9cThin Film Magnetoresistors In Memory, Storage, and Related Applicationsxe2x80x9d, IEEE Trans. on Mag., Vol. Mag 11, P 1039-1050, (July 1975). In a magnetic head using the AMR effect, longitudinal bias is often applied in order to suppress the Barkhausen noise. The longitudinal bias may be realized by an antiferromagnetic material such as FeMn, NiMn, nickel oxide or the like.
Furthermore, more remarkable magneto-resistivity has been disclosed. That is, the resistance change of a layered magnetic sensor is based on a spin dependent transmission of conductive electrons between magnetic layers via a non-magnetic layer and accompanying spin dependent scattering on the layer boundary. Such a magneto-resistivity is called giant magneto-resistivity, spin-valve effect, and the like. Such a magnetoresistive sensor is made from an appropriate material and enables one to improve the sensitivity and increase the resistance change in comparison with a sensor using the AMR effect.
In this type of magnetoresistive sensor, the resistance of a plane between a pair of ferromagnetic layers separated by a non-magnetic layer changes in proportion to the cosine of an angle defined by the magnetization directions in the two ferromagnetic layers.
On the other hand, U.S. Pat. No. 4,949,039 (corresponding to EPO Patent Publication 0 346 817A2 published on Dec. 20, 1989 and Japanese Patent Publication 2-61572 dated Mar. 1, 1990) discloses a layered magnetic configuration which brings about a high magneto-resistance change generated by parallel or anti-parallel arrangement of magnetization in the magnetic layers. The layered configuration is made from ferromagnetic transition metals or alloys.
Magnetoresistive sensors including semiconductor material and electrodes are also disclosed.
A magnetoresistive element including Van der Pauw configuration semiconductor element is shown in C. M. Wolfe, et al., xe2x80x9cHigh Apparent Mobility in Inhomogeneous Semiconductorsxe2x80x9d, Solid State Science and Technology, pp 250-255 (February 1972).
U.S. Pat. Nos. 5,696,655, 5,699,215, 5,965,283 disclose a magnetoresistive sensor (see FIG. 1) composed of basic elements of high electron mobility semiconductor 3 and electrodes 1, 2 which define a sense current path through the high electron mobility semiconductor 3 and detect the voltage between electrode 1 and electrode 2.
As representative magnetoresistive elements including a high electron mobility semiconductor 3, a Corbino type element and a Van der Pauw element are known.
FIG. 1 shows a representative Corbino type element. The shape of this kind of element is typically a cylinder. There are two electrodes, electrode 1 is in the cylinder and electrode 2 is on the outer surface of the cylinder. The space between the two electrodes is filled with high electron mobility semiconductor 3.
FIG. 2 shows a representative Van der Pauw type element. This kind of element typically consists of a cylindrical high electron mobility semiconductor 11 mounted on a substrate 13. A high electron conduction material 10 is buried in the cylindrical high electron mobility semiconductor 11. The element includes a pair of electrodes 12 which make a current path in the cylindrical high electron mobility semiconductor 11 and in the high conduction material 10, and another pair of electrodes 12a to detect the voltage induced by the current to generate a magnetic field 14 for detection.
These two types of elements exhibit a magnetoresistive change typically like that shown in FIG. 3. The resistance of an element is minimum when an applied field is near zero. The resistance of an element increases when an applied field increases in either the plus direction or the minus direction. The low field magneto-resistance is quadratic. It is necessary to provide over 0.1 T biasing, or if permitted over 0.2 T biasing, to a) distinguish the direction of the applied field (e.g. up or down), b) to enhance the sensitivity of the sensor and c) to obtain a linear response close to an external field H=0. Then, it is important to add or attach an entity which generates a biasing magnetic field, to the element, in order to use it as a magnetic read head.
However, it is not sufficient to add as large a biasing magnetic field as possible. There is a limit to the biasing magnetic field value, because too large a biasing magnetic field may cause a reversal of magnetization of a recording media and destroy pre-recorded data. Thus, it is also important that a biasing magnetic field be below the field value leads to a destruction of data.
The magnetoresistive sensor includes a magnetoresistive element and equipment which generates a magnetic field in the magnetoresistive element thereby inducing a biasing magnetic field in the element, where the magnetoresistive element comprises a high electron mobility semiconductor and electrodes which are connected to the semiconductor.
If it is an insulator, the equipment, which generates the biasing magnetic field and supplies it to the magnetoresistive element, may contact directly to the magnetoresistive element. If it is a conductor, an insulating separation layer must be set between the equipment and the element.
A magnetoresistive element is representatively Corbino disk type or a bar type magnetoresistive element. Another candidate of the magnetoresistive element is an element consisting of a high electron mobility semiconductor, a pair of electrodes which make a current path in the high electron mobility semiconductor, and another pair of electrodes to detect the induced voltage by the current.
The value of the magnetic field applied from the equipment to the element is over 1 kOe, preferably over 2 kOe.
The magnetoresistive sensor is used as a part of a reproducing head in two types of magnetic recording/reproducing systems. One is a system where a magnetization direction in a recording media magnetic domain bit is parallel or anti-parallel to the moving direction of the media. Another one is a system where a magnetization direction in a recorded magnetic domain bit in a recording media is perpendicular or nearly perpendicular to the surface of the media. In either system, the amplitude of a magnetic field on the surface of the recording media induced by the equipment has to be smaller than one where the magnetic domain wall of a pre-recorded magnetic domain bit starts to move. In that case, the amplitude of the magnetic field applied from the equipment to the medium is less than the coercive force and reversal field of the medium.
The coercive force of the medium should be larger than 3 kOe, preferably larger than 5 kOe. A part of the upper or lower pole of a recording head in the recording/reproducing system is made from a magnetic material in which the saturation magnetization is larger than 1.8T. NiFeCo alloy is suitable for this material.
The magnetic recording/reproducing apparatus according to the present invention comprises: a magnetic recording medium having a plurality of tracks for recording data; a magnetic recording head for storing data in the magnetic recording medium; the magnetoresistive head; and actuator means for moving the magnetic recording head and the magnetoresistive head to a desired track on the magnetic recording medium.
Moreover, the magnetic recording medium may be a hard disk.